A developer for developing an electrostatic latent image in electronic photography, electrostatic recording, electrostatic printing, and the like, is first adhered to an image supporting object such as an electrostatic latent image supporting object on which the electrostatic latent image is formed in a development process. The developer is then transferred to a transfer medium such as from the electrostatic latent image supporting object in a transfer process; and then the developer is fixed to the paper in a fixing process. Here, the developer for developing the electrostatic latent image formed on the latent image supporting object includes a two-component system developer that consists of a carrier and a toner, and a single component system developer such as a magnetic toner and a non-magnetism toner that do not include the carrier.
Conventionally, dry toner is used for electronic photography, electrostatic recording, electrostatic printing, and the like, where the dry toner is the so-called ground type toner that is made of a toner binder (such as styrene system resin and a polyester system resin) and a colorant that are melt-kneaded and ground (pulverized).
Recently and continuing, so-called polymerization type toners are being examined for the developer. The polymerization type toners are produced by a toner manufacturing process including a suspension polymerization method, and an emulsion polymerization condensing method. In addition, a polymer dissolution suspending method is also being examined, where the method generates a volumetric shrinkage (Patent Reference 1). According to this method, a toner material is dispersed and dissolved in volatile solvents, such as a low boiling-point organic solvent; emulsified and made into droplets in an aquatic medium that contains a dispersant; then the volatile solvent is removed. This method provides great flexibility concerning resins, and is applicable to a polyester resin unlike the suspension polymerization method and the emulsion polymerization condensing method. The polyester resin is desirable in a full color process where transparency, flat, and smooth natures of an image after fixing are required.
However, according to the conventional methods of manufacturing the polymerization type toner, it is premised that the dispersant be used in the aquatic medium. The dispersant, which spoils the charging characteristic of the toner, tends to remain on the surface of the toner to degrade environmental stability. Accordingly, it is attempted that the dispersant be washed away; for this, a great amount of water is required. For this reason, the methods are not necessarily satisfactory.
Another conventional practice uses a spray drying method for manufacturing the toner, wherein an aquatic medium is not used (Patent Reference 2). According to this method, an atomizer produces particles by ejecting one of melting liquid of toner material and liquid wherein toner-containing liquid is dissolved. Then, the ejected particles are dried to obtain toner particles. Accordingly, the problem due to using the aquatic medium is not generated.
Nevertheless, the toner particles obtained by the conventional spray granulating method are comparatively coarse and large; and particle size distribution is also great. That degrades characteristics of the toner.
Then, in an attempt to replace the conventional practices, Patent Reference 3 proposes a method and an apparatus for manufacturing the toner. According to this method, minute droplets are formed by using a piezo-electric impulse, and the droplets are dried. Further, Patent Reference 4 proposes a method of forming minute droplets by using thermal expansion in a nozzle; the formed droplets are dried.    [Patent reference 1] JPA H7-152202    [Patent reference 2] JP S57-201248    [Patent reference 3] JP 3786034    [Patent reference 4] JP 3786035
Nevertheless, according to the toner manufacturing method and apparatus proposed by Patent References 3 and 4, one piezo-electric object causes discharging droplets from only one nozzle, that is, the number of droplets that are discharged in a unit time is relatively small, and the productivity is low.
Then, the applicant of the present invention has disclosed toner manufacturing methods and apparatuses by Patent References 5 and 6. According to Patent Reference 5, a nozzle is vibrated by expansion and contraction of a piezo-electric object so that droplets of toner containing fluid are discharged at a fixed frequency, then the droplets are solidified to become toner. According to Patent Reference 6, a discharging member having a discharging hole, and a vibration unit are included, wherein the discharging member is vibrated by the vibration unit so that droplets are discharged from the discharging hole; then, the droplets are dried and solidified to make the toner particles.    [Patent Reference 5] JPA 2006-293320    [Patent Reference 6] JPA 2006-297325
Nevertheless, according to Patent Reference 5, the piezo-electric object faces the circumferential edge of the nozzle, and vibrates the nozzle by expansion and contraction of the piezo-electric object; then, only a domain of the nozzle is vibrated, which domain corresponds to an opening of the piezo-electric object. That is, a sufficient displacement of the nozzle is not obtained. Accordingly, when discharging the toner-containing liquid 10 that has a great viscosity (for example, 10 mPa·s) containing a great amount of solid components, the nozzle tends to be clogged, that is, the toner cannot be stably and efficiently produced. In addition, although Patent Reference 6 discloses a technique of vibrating a droplet discharging unit with a piezo-electric object, it does not disclose any specific configuration, and its scope does not exceed Patent Reference 5.